<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>单位的辨析</title>
    <style>
        .div1{
            width:15em;
            height:15em;
            background-color: green;
        }
        .div2{
            width:15rem;
            height:15rem;
            background-color: fuchsia;
        }
        .div3{
            width:15ex;
            height:15ex;
            background-color: blueviolet;
        }
        .div4{
            width:15ch;
            height:15ch;
            background-color: blue;
        }
    </style>
</head>
<body>
<div class="div1"></div>
<div class="div2"></div>
<div class="div3"></div>
<div class="div4"></div>
</body>
</html>